There have been proposed a variety of kinds of systems, such as a curve overspeed warning system (CSWS), an auto cruise control system (ACC), a lane keeping assistance system (LKA), a pre-crash safety system (PCS), etc., which serve to support the driving or operation of a vehicle. In such technologies, there has been known, for example, a system in which a curve and an obstacle existing on a travel path of an automotive vehicle are detected, and an optimum speed of the vehicle is calculated based on obstacle information and curve information, so that in cases where the speed of the vehicle is larger than an optimum speed, the vehicle is decelerated to the optimum speed by controlling a throttle mechanism and an automatic transmission (for example, refer to a first patent literature).
There is also a system which is provided with a unit for calculating a curvature of a road at every instant and a unit for controlling the speed of own vehicle, wherein when the curvature of the road at every instant tends to increase, the speed of the own vehicle is caused to decrease, whereas when the curvature at every instant tends to decrease, the speed of the vehicle is caused to increase (for instance, refer to a second patent literature). In addition, there have also been known a technology in which the shape of a road is acquired by a road shape acquisition unit, so that the radius of curvature of the road is calculated, and a technology in which in cases where the speed of an automotive vehicle is excessively high, the speed of the vehicle is decelerated from just before a curve, or a warning is issued, based on the radius of curvature thus calculated.
However, an actual driver often carries out driving in such a manner that he or she drives at a comparatively high speed in a straight line course, decelerates just before a curve, and accelerates after the end of the curve, in a repeated manner. Accordingly, even if the speed of a vehicle before the curve is higher than an optimum speed, as long as the vehicle speed is able to be decelerated to the optimum speed immediately before the curve, there will be no problem from the point of view of safe driving, so it might be an annoyance to the driver to limit the vehicle speed or to issue a warning only according to the radius of curvature of the curve, as referred to above.